Biofilm Formation among Staphylococcus epidermidis Strains Isolated from Healthy People in Isfahan

Staphylococcus epidermidis is known as the normal flora residing in the human skin unlike Staphylococcus aureus lacks different virulence factors of pathogenesis, so biofilm formation should be considered as the unique pathogenic element in these bacteria. Prevalence of biofilm producing strains in healthy people could be a significant health challenge. The aim of this study was the isolation and phenotypic and genotypic analysis of biofilm formation among S. epidermidis strains isolated from healthy people samples in Isfahan, Iran during 2016. Sampling was carried out from 100 healthy people and all isolated strains were identified at the species level using specific primers and their ability to form biofilm was determined using combination of qualitative Congo-Red agar and quantitative microtiter plate assay. In addition the presence of icaABCD, aap and IS256 genes was detected by polymerase chain reaction (PCR). Using PCR, all 123 isolated strains were confirmed as S. epidermidis strains. The quantitative biofilm assay showed that 12.2% of strains were able to attach strongly to polystyrene microplates. On the other hand, 6.5% of S. epidermidis strains, respectively, were able to form black colonies on Congo-red agar plates and were slime positive. The presence of icaA, icaB, icaD, IS256 and aap genes was limited to 3.3, 3.3, 3.3, 0 and 52 % of strains. The results of this study are indicated the spread of biofilm producing and antibiotics resistance Staphylococcus epidermidis strains among healthy people in Isfahan city. Due to the fact that S. epidermidis strains are usually considered as the contaminant strains in the clinical samples, precise diagnosis of these strains in the clinical samples can be a great help to the specialists in diagnosing clinical infections. Presence of icaA and icaD genes with high prevalence of aap gene among biofilm producing S. epidermidis strains suggests that ica, aap and biofilm forming ability occur jointly in specific S. epidermidis clones and spread preferentially in the hospital and community.